Unsteady interaction between shear layer vortices and a bow shock during supersonic injection

Sonic, underexpanded helium jets were transversely injected through a turbulent boundary layer into a supersonic Mach 3 flow. Schlieren images were obtained using a high speed camera to visualise the mean and instantaneous flow features. Wall-pressure fluctuations along the gas injection centerline were measured using flush-mounted high-speed pressure transducers. The jet-to-crossflow momentum ratios ranged from 1.21 – 3.89, while the pressure ratios (jet exit to mean flow) were 17.41 – 56.12. Mean Schlieren images show that the penetration depth increases with momentum flux ratio. Instantaneous images reveal a highly unsteady interaction between shear layer vortices and adjacent shock structures. Periodic shear layer vortices were generated via the Kelvin–Helmholtz instability mechanism and convected downstream. Time varying deformation of the λ shock were due to the separated incoming boundary layer and the interaction of the bow shock with shear layer vortices. Compression waves are also observed propagating along the shear layer in the direction of flow convection.